The Pseudomonas aeruginosa Secretory Product Pyocyanin Inactivates α1 Protease Inhibitor: Implications for the Pathogenesis of Cystic Fibrosis Lung Disease

摘要

α₁ Protease inhibitor (α₁PI) modulates serine protease activity in the lung. Reactive oxygen species inactivate α₁PI, and this process has been implicated in the pathogenesis of a variety of forms of lung injury. An imbalance of protease-antiprotease activity is also detected in the airways of patients with cystic fibrosis-associated lung disease who are infected withPseudomonas aeruginosa. P. aeruginosa secretes pyocyanin, which, through its ability to redox cycle, induces cells to generate reactive oxygen species. We tested the hypothesis that redox cycling of pyocyanin could lead to inactivation of α₁PI. When α₁PI was exposed to NADH and pyocyanin, a combination that results in superoxide production, α₁PI lost its ability to form an inhibitory complex with both porcine pancreatic elastase (PPE) and trypsin. Similarly, addition of pyocyanin to cultures of human airway epithelial cells to which α₁PI was also added resulted in a loss of the ability of α₁PI to form a complex with PPE or trypsin. Neither superoxide dismutase, catalase, nor dimethylthiourea nor depletion of the media of O₂ to prevent formation of reactive oxygen species blocked pyocyanin-mediated inactivation of α₁PI. These data raise the possibility that a direct interaction between reduced pyocyanin and α₁PI is involved in the process. Consistent with this possibility, pretreatment of α₁PI with the reducing agent β-mercaptoethanol also inhibited binding of trypsin to α₁PI. These data suggest that pyocyanin could contribute to lung injury in the P. aeruginosa-infected airway of cystic fibrosis patients by decreasing the ability of α₁PI to control the local activity of serine proteases.